Self-expression is a very important human need, though often overlooked because it typically is a latent need, one that is present but rarely referred to explicitly. Examples are fashion, acting or performing, where the emphasis clearly is on showing something about oneself to others, but also new forms of self expression are emerging, like blinging (abundant decoration of mobile phones) and blogging (expressing one's views or daily experiences to the entire world on the internet).
One of the earliest forms of self expression is writing: autobiographies, letters, diaries. In written (or typed) text, experiences can be recorded by careful selection of words and sentences. What cannot be easily recorded however, is the mood of the writer at the moment of writing. Publication U.S. Pat. No. 6,375,622 B1 describes a writing brush with one or more biological sensors embedded in or attached to the shaft of the writing brush. The biological sensors record the biological activities of the user that are associated with the user's sensory, perceptual, emotional, cognitive and physiological conditions during writing or drawing. The sensory signals from the detectors provide ongoing information of the user's graphonomic act and thus enable the user to control and regulate his or her bodily conditions throughout the writing process by influencing the changes of the sensory signals. The writing pen is used for Chinese brush writing which is known as an art capable of achieving emotional stabilization and mental relaxation. However, the user cannot express his or her mood other than in the text written. Yet such a need clearly exists, as evidenced by the use of for example smileys in e-mail, sometimes crucial to convey the correct message (to indicate one is serious, or joking etc.). The latter method is rather cumbersome because the writer has to include explicitly such mood indicators in the text.